1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to a method and apparatus for transmitting and receiving reverse feedback information in a wireless packet data communication system using Multi Input Multi Output (MIMO).
2. Description of the Related Art
Mobile communication systems have evolved into high-speed, high-quality wireless packet data communication systems to provide data services and multimedia services beyond the early voice-oriented services. Recently, various mobile communication standards, such as High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), both defined in the 3rd Generation Partnership Project (3GPP), High Rate Packet Data (HRPD) defined in the 3rd Generation Partnership Project-2 (3GPP2), and 802.16 defined in IEEE, have been developed to support high-speed, high-quality wireless packet data communication services.
The existing 3rd Generation wireless packet data communication systems, such as HSDPA, HSUPA and HRPD, use technologies such as an Adaptive Modulation and Coding (AMC) method and a Channel-Sensitive Scheduling method to improve transmission efficiency. With the use of the AMC method, a transmitter can adjust the amount of transmission data according to the channel state. That is, when the channel state is not ‘Good’, the transmitter reduces the amount of transmission data to adjust the reception error probability to a desired level, and when the channel state is ‘Good’, the transmitter increases the amount of transmission data to adjust the reception error probability to the desired level, thereby efficiently transmitting a large volume of information.
With the use of the Channel-Sensitive Scheduling-based resource management method, the transmitter selectively services the user having a better channel state among several users, thus increasing the system capacity compared to the method of allocating a channel to one user and servicing the user with the allocated channel. Such capacity increase is known as ‘multi-user diversity gain’. In sum, the AMC method and the Channel-Sensitive Scheduling method each are a method of applying an appropriate modulation and coding scheme at the most-efficient time determined depending on partial channel state information fed back from a receiver.
To realize the AMC method and the Channel-Sensitive Scheduling method, the receiver should feed back the channel state information to the transmitter. The channel state information that the receiver feeds back is referred to as ‘Channel Quality Information (CQI)’.
Recently, intensive research is being conducted to replace Code Division Multiple Access (CDMA), the multiple access scheme used in the 2nd and 3rd Generation mobile communication systems, with Orthogonal Frequency Division Multiple Access (OFDMA) in the next generation system. 3GPP and 3GPP2 have started their standardizations on the evolved systems employing OFDMA. It is known that the OFDMA scheme, compared to the CDMA scheme, can expect a capacity increase. One of the several causes bringing about the capacity increase in the OFDMA scheme is that the OFDMA scheme can perform scheduling in the frequency domain (Frequency Domain Scheduling). As though the transceiver acquires capacity gain according to the time-varying channel characteristic using the Channel-Sensitive Scheduling method, the transceiver can obtain higher capacity gain with use of the frequency-varying channel characteristic. However, to support Frequency Domain Scheduling, the transmitter should previously acquire channel state information separately for each frequency. That is, the transmitter needs CQI feedback separately for each frequency, causing an increase in the CQI feedback load.
In the next generation system, intensive research is being conducted on the introduction of Multiple Input Multiple Output (MIMO) technology employing multiple transmit/receive antennas. The term ‘MIMO’ as used herein refers to a technology that simultaneously transmits multiple data streams over the same resources using multiple transmit/receive antennas. It is known that when the channel state is ‘Good’, it is possible to increase the throughput at the same error probability by transmitting multiple low-modulation order data streams rather than increasing the modulation order of the data streams.
In the MIMO technique, the dimension over which an individual data stream is transmitted is called as a ‘layer’, and the method that applies AMC separately according to the channel state of the layer is efficient in increasing the capacity. For example, Per Antenna Rate Control (PARC) is a technology in which every transmit antenna transmits a different data stream, and in this technology, the layer is a transmit antenna. Data streams transmitted via the multiple transmit antennas experience different channels, and the PARC technique applies AMC such that a larger amount of data can be transmitted via the transmit antenna having a good channel state and a less amount of data can be transmitted via the transmit antenna having a poor channel state. As another example, there is Per Common Basis Rate Control (PCBRC), and in this technology, the layer is a fixed transmission beam. Therefore, the PCBRC technique transmits a greater amount of data over the transmission beam with a good channel state, and transmits a less amount of data over the transmission beam with a poor channel state.